/*
 * Copyright 2011-2012 by The Regents of the University of California Licensed
 * under the Apache License, Version 2.0 (the "License"); you may not use this
 * file except in compliance with the License. you may obtain a copy of the
 * License from
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package edu.ucsd.db.bassarisk.query.expression.visitor;

import java.util.ArrayList;
import java.util.List;

import edu.ucsd.db.bassarisk.exception.VisitorException;
import edu.ucsd.db.bassarisk.query.expression.Expressions.Expression;
import edu.ucsd.db.bassarisk.query.expression.Expressions.KeywordMatchExpr;
import edu.ucsd.db.bassarisk.query.expression.Expressions.NonterminalExpr;

/**
 * A base class for simple transformations over the query expression tree.
 * Performs the default transformations on the base classes, and allows
 * extending types to only override the visit method for the concrete expression
 * types involved in the specific transformation.
 * 
 * @param <A>
 */
public class ExpressionTreeTransformation<A> extends
    SupertypeDeferingExpressionTreeVisitor<Expression, A> {
  @Override
  public Expression visitKeywordMatchExpr(final KeywordMatchExpr expr, final A arg)
      throws VisitorException {
    return expr;
  }

  @Override
  public Expression visitNonterminalExpr(final NonterminalExpr expr, final A arg)
      throws VisitorException {
    List<Expression> oldSubExprs = expr.getSubExprs();
    List<Expression> newSubExprs = new ArrayList<Expression>();
    for (Expression subExpr : oldSubExprs) {
      newSubExprs.add(subExpr.accept(this, arg));
    }
    return expr.transform(newSubExprs);
  }
}
